Screwstrips are known whereby the screws are connected to each other by a retaining belt preferably of plastic material. Screws in such strips are engaged by a bit of a screwdriver and then screwed into a workpiece. In the course of the bit engaging the screw and/or driving the same into the workpiece, the screw becomes attached from the plastic strip.
Known screwstrips of this type are disclosed in Canadian Patent 1,040,600, issued Oct. 17, 1978 to Schwartz; U.S. Pat. No. 4,167,229 to Keusch et al, issued Sep. 11, 1979; U.S. Pat. No. 4,930,630 to Habermehl, issued Jun. 5, 1990; U.S. Pat. No. 5,758,768 to Habermehl, issued Jun. 2, 1998 and U.S. Pat. No. 5,819,609 to Habermehl, issued Oct. 13, 1998, the disclosures of which are incorporated herein by reference.
Screws carried by such strips are adapted to be successively incrementally advanced to a position in alignment with and to be engaged by a bit of a reciprocating, rotating power screwdriver and screwed into a workpiece. In the course of the bit engaging the screw and driving it into a workpiece, the screw becomes detached from the plastic strip leaving the strip as a continuous length.
In the use of such collated screwstrips in screwdrivers, the strip serves a function of assisting in guiding the screw into a workpiece and to accomplish this, the strip is preferably retained against movement towards the workpiece. In the strip, each screw to be driven has its threaded shaft preferably threadably engaged in a threaded sleeve of the strip such that on the screwdriver engaging and rotating each successive screw, the screw turns within the sleeve which acts to guide the screw as it moves forwardly into threaded engagement into the workpiece. Preferably, only after the tip of the screw becomes engaged in the workpiece, does the head of the screw come into contact with the sleeve. Further forward movement of the screw into the workpiece then draws the head downwardly to engage the sleeve and rupture the sleeve by reason of the forward movement of the head with the strip retained against movement towards the workpiece. The sleeve is preferably configured to have fragible straps which break on the head passing through the sleeve such that the strip remains intact as a continuous length. Since the strip is a continuous length, on advancing the strip with each successive screw to be driven, it necessarily results that portions of the strip from which each screw has been driven are also advanced to exit from the power screwdriver.
Known power screwdrivers for driving said collated screwstrips include U.S. Pat. No. 4,146,071 to Mueller, issued Mar. 27, 1996; U.S. Pat. No. 5,568,753 to Habermehl, issued Oct. 29, 1996; U.S. Pat. No. 5,870,933 to Habermehl, issued Feb. 16, 1999 and U.S. Pat. No. 5,570,618 to Habermehl et al., issued Nov. 5, 1996.
Each of these patents teach an automatic feed screwdriver in which a housing is fixably secured to a power screwdriver. A slide body is provided reciprocally slidable relative the housing and an extension spring is provided so as to bias the slide body outwardly relative the housing. The slide body carries a screw feed channel to receive the screwstrips and via which the screws held in the screwstrips are advanced radially to a point where each successive screw to be driven is coaxially arranged within a bore of a guide tube coaxially in line with a driver shaft. These prior art auto feed screwdrivers provide for various linkages between the slide body and the housing such that on reciprocal telescopic sliding of the slide body into and out of the housing between extended and retracted positions, the linkages cause automatic advance of the screwstrip in the feed guide channel. The relative timing of the advance of the screwstrip is thereby timed and linked to the relative position of the slide body in the housing in a complete cycle of movement from an extracted position to a retracted position and back to the extended position.
These prior art devices have the disadvantage that they must provide both a housing and a slide body and for an appropriate linkage between the two in order for automatic advance of the screwstrip in a desired manner.
Such known auto feed screwdriving tools have the disadvantage that they require relatively large number of parts, that they require a housing which is adapted to be physically coupled to the power driver tool, that they require a mechanism for linking of the slide body to the housing, that they require an extension spring which typically needs to be relatively substantial to bias the slide body to an extended position out of the housing, that on using a device, a user must, to drive a screw, overcome the relatively substantial forces of the extension spring biasing the slide body to the extended position out of the housing and that the forces which are applied to advance the screwstrip are frequently limited either to springs provided in the devices for such purpose or to levered forces which can be developed by the linkages between the slide body and the housing.
These previously known auto feed devices suffer the disadvantage of being relatively complex, expensive and not readily adapted for the production as an inexpensive consumer tool.